This invention relates to a focus ring useful for focusing plasma in a plasma processing apparatus.
In semiconductor fabrication, process gases are used to deposit material upon, etch, or clean semiconductor substrates. These processes are typically carried out in an enclosed process chamber having gas distributors for distributing process gas therein. One problem with conventional process chambers is the inability to achieve a uniform distribution or concentration of reactive process gas species across the substrate surface, particularly at the perimeter of the substrate. The non-uniform distribution of reactive process gas species results in non-uniform and variable processing rates across the substrate surface. A more uniform reactive species distribution across the substrate is obtained using process gas flow containment structures to direct the flow of process gas onto the substrate. For example in plasma processing, it is known to use a plasma focus ring around the substrate to maintain a more uniform distribution of the reactive process gas species across the substrate.
Conventional plasma and process gas focus rings typically comprise a wall surrounding the substrate for directing the flow of process gas or plasma on the surface of the substrate. One problem with such focus rings arises from the deposition of contaminant polymeric and other process byproduct deposits on the walls of the focus rings, and in particular the inner wall facing the substrate. The contaminant particles also deposit on the interior walls and other process components of the chamber. The contaminant deposits are formed from the decomposition and/or chemical recombination of chemical species in the process gas plasma, for example, polymeric materials comprising carbon, nitrogen, and hydrogen species. These deposits flake off and produce particulates that contaminate the substrate during processing or manipulation of the substrate. It is difficult to non-destructively detect contamination of the substrates during processing, and it is only in the final processing stages that the contaminants are discovered, and the entire substrate is rejected. Thus, the focus ring, interior of the chamber, and other processing components must be regularly cleaned thereby reducing overall process efficiency. Also, many of these cleaning processes are performed using corrosive gases, such as NF.sub.3 plasmas, which erode the processing components and limit the life of the process chamber.
In another solution for reducing particulate contamination involves a final processing step of raising the focus ring above the substrate and flowing inert gas in the chamber to flush out the contaminant particulates accumulated in this region, as for example, disclosed in commonly assigned U.S. Pat. No. 5,423,918. However, mechanical stresses resulting from raising and lowering the focus ring can dislodge the contaminant deposits formed on the focus ring to form additional contaminant particulates in the chamber. Also, the steps of raising and lowering the focus ring increase process time and further reduce efficiency.
Thus, there is a need for a processing apparatus capable of providing a substantially uniform concentration of reactive process gas across the substrate surface, and in particular, at the perimeter of the substrate. There is also a need for an apparatus and method that reduces formation or deposition, of contaminant particulate deposits on the chamber walls and processing components.